Abstract: In this study, the morphologies of Falcula media Voigt, Falcula semiundulata Voigt and Pseudofalcula hyalina (Takano) Gómez, Wang & Lin were observed by scanning electron microscopy (SEM), and the ultrastructural differences between the two diatom genera Falcula and Pseudofalcula were compared. Furthermore, we also briefly discussed the habits of these two diatom genera. The results show that: (1) F. media is a newly recorded diatom species in China. (2) Both the frustules of Falcula and Pseudofalcula are arcuate, but they are significantly different in frustules sizes, widths of the sterna, densities of transapical striae and structures of the apical pore fields. (3) Species of Falcula are mainly epiphytic diatoms attached to seaweeds, while Pseudofalcula is a typical epizoic diatom genus and its hosts are mostly marine copepods. Our study expands the geographic distribution of F. media, F. semiundulata and P. hyalina, and provides important reference information to distinguish the genera Falcula and Pseudofalcula.